A fourth generation (4G) communication system, which is a next-generation communication system, is under development to provide users with services of various Quality of Service (QoS) levels at a data rate of about 100 Mbps. Particularly, the 4 G communication systems are advancing in order to support high speed services by guaranteeing mobility and QoS in Broadband Wireless Access (BWA) communication systems such as wireless Local Area Network (LAN) systems and wireless Metropolitan Area Network (MAN) systems. Representative communication systems include an Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system.
In the IEEE 802.16 system, a Channel Quality Indicator (CQI) channel indicates an uplink subchannel used to periodically transmit a radio channel quality measured by a terminal, to a base station. That is, the base station receives the CQI from the terminal and thus determines a Modulation and Coding Scheme (MCS) to apply to downlink traffic transmission using the CQI. For doing so, the terminal is assigned a CQI channel from the base station. The CQI channel allocation is carried out using Information Element (IE) for allocating the CQI channel, in an uplink map message. According to the IEEE 802.16 standard, the CQI channel is allocated according to a period and a duration. That is, the CQI channel is periodically allocated for the duration through one-time allocation information transmission.
The IEEE 802.16 system defines a sleep mode to facilitate scheduling of the base station and to reduce power consumption of the terminal. The sleep mode divides an operation time of the terminal to a sleep window and a listening window, and controls to suspend the communication of the terminal suspends during the sleep window and to perform the communication of the terminal only in the listening window. The entry to the sleep mode is accomplished the request of the terminal and the acceptance of the base station, or the instruction of the base station.
Since the CQI channel is allocated periodically for the defined duration, the entry to the sleep mode when the CQI channel is already allocated hinders management of the CQI channel. That is, even when the CQI channel is allocated on the periodic basis, the CQI channel in the sleep window is wasted because the terminal does not communicate during the sleep window. When the CQI channel is deallocated at the same time as the sleep mode entry in order to avoid the waste, it is necessary to allocate the CQI channel for the communication in the listening window and to deallocate the CQI channel as the listening window ends. That is, the repetitive CQI channel allocation/deallocation in every listening window increases signaling overhead.
While the CQI channel and the sleep mode are defined for the sake of the efficient operation of the communication system, the CQI channel management is ambiguous in the sleep mode entry as discussed above. Hence, what is needed is a method for minimizing the resource waste and the signaling overhead by effectively operating the CQI channel in the sleep mode.